The invention relates to a method for creating a puncture wound for obtaining a sample of body fluid from a body part and to a suitable handheld apparatus, comprising a puncture element, a drive by which the puncture element is movable in a direction towards the skin and in a direction away from the skin, and a control unit for controlling the movement of the puncture element.
For withdrawing a small amount of blood or interstitial fluid from a body part, e.g., a finger, for analytical diagnostic purposes, puncture elements, e.g., needles or lancets, are used to puncture the corresponding body part, thereby generating a puncture wound. Specially trained personnel are required when this is done manually. Nevertheless, such a puncture is still associated with considerable pain.
Blood-sampling systems comprising a puncture device and the respective lancets adapted specifically to the particular device have been in use for a long time. A housing of the puncture device holds a drive capable of moving the puncture element in the direction towards the skin and in the direction away from the skin. A spring is used as the drive element for the puncture movement. Early in the development of such devices, very simple designs were customary in which the lancet was attached directly to one end of a compression spring arranged in an elongated housing (e.g., U.S. Pat. No. 4,469,110).
However, such blood-sampling systems do not fulfill the high demands that must be met when regular monitoring of analytical blood values is required. This is particularly true for diabetics, who should monitor their blood sugar level frequently to be able to keep it within certain limits by means of insulin injection or dietary controls. Extensive scientific study has shown that a dramatic reduction in extremely severe late consequences of diabetes mellitus (e.g., retinopathy with the resulting blinding of the patient) can be achieved by intensive therapy with at least four blood tests per day.
This intensive therapy requires that generation of the blood sample causes the least possible pain. Numerous different blood-sampling systems have been developed with the goal of achieving an improvement in this regard.
To achieve blood sampling with the least possible pain it is considered essential that the puncture-and-return movement of the puncture element should be as fast as possible, without vibration and with an optimal puncture depth. An optimal puncture depth is considered here to be a depth no greater than that which is absolutely necessary to reach blood-carrying layers of tissue.
A handheld apparatus of the type described in US 2004/0092996 allows relatively painless blood sampling. In such a handheld apparatus, the drive comprises a drive spring for creating a drive force and a drive rotor that executes a rotational movement driven by the drive force. Rotational movements of the drive rotor are converted into a puncture-and-return movement of the puncture element by a control unit comprising a curve control linked to the drive rotor.
Furthermore, electric puncture devices are known, for example, from U.S. Pat. No. 6,364,889. Here a puncture-and-return movement of the lancet is driven by the magnetic force of a coil. Electric puncture devices have the advantage that the speed of the puncture element can be controlled with high precision. WO 03/088824 recommends in this regard that in a puncture movement the stratum corneum be punctured at a maximum speed and that the lancet then be decelerated, so that penetration into deeper layers of the skin takes place at a lower speed. Such a puncture movement, in which the lancet speed is reduced with the depth of penetration, aims to reduce painful pressure waves.
Despite the extensive development work that has led to the designs mentioned above and numerous other constructions, there still remains great interest in sample collection systems and methods which fulfill as far as possible the difficult and sometimes contradictory requirements (minimal pain perception, reliable collection of a sufficient quantity of sample, simple operability, compact design, inexpensive construction) simultaneously.